Previously, yellow and silver eel series have been analyzed by WGEEL through trend analysis (ICES 2021a). Here, we have chosen to concentrate on improving the trend analysis for the silver eel time series.
In the 2023 data call, 57 silver eel time series were available, located in 15 countries (Figure @ref(fig:mapsilverall)). The majority of these series are from Lithuania (9 series), Netherlands (7 series), United Kingdom (6 series) and France (6 series). Four time series (BI1S, BI4S, NSIS, PanS) are international trawling surveys. Data on these silver eel time series have been added to the WGEEL database in the past, but as these international series have no dedicated reporting country, their data have not been inserted into the database for recent years.
Map of available silver time series. Updated time series correspond to time series for which at least one value was provided for years the three last years
Category | Available data | Missing data |
|---|---|---|
Nb of series >=10 years | 30 | 27 |
Nb of series with quality id | 36 | 21 |
Nb of series with habitat data | 57 | 0 |
Nb of series with sampling type | 53 | 4 |
Nb of series with effort data | 23 | 34 |
Nb of series with gear | 56 | 1 |
Nb of series with restocking data | 56 | 1 |
Nb of series with distance to sea | 52 | 5 |
Summary of available silver eel series per country, including whether they were kept or dropped for the trend analysis. Habitat: C = coastal water, F = freshwater, MO = marine water (open sea), T = transitional water (according to WFD); gear: 226 = fyke nets, 227 =stow nets, 228 = barriers, fences, weirs, etc., 230 = traps, 234 = longlines, 242 = electric fishing, 245 = gear unknown; sampling type: 1 = commercial catch, 2 = commercial CPUE, 3 = scientific estimate, 4 = trapping all, 5 = trapping partial gear; quality id: 0 = series has ended and no future data will become available, 1 = good quality data; stocking: FALSE = no impacts of stocking, TRUE = impacts of stocking; and ecoregion: WM = Western Mediterranean Sea, BS = Baltic Sea, NS = Greater North Sea, IB = Bay of Biscay and the Iberian Coast, CS = Celtic Seas, AL = Aegean-Levantine Sea, CM = Ionian Sea and the Central Mediterranean Sea, AS = Adriatic Sea. For all, NA means not available (no information provided).
A summary of the type of data available in the available silver eel time series is given in Table @ref(tab:tablesummary) and Figure @ref(fig:figureseriessummary), and a detailed summary of all the series is presented in Annex x.x. From all available silver eel time series, 30 series have 10 or more years of available data. Only 23 of the 57 series have effort data submitted. Most silver eel series were collected in freshwaters via traps and fyke nets. In terms of sampling type, 14 series were from commercial catches, 5 series was reported as commercial CPUE, 10 were assigned as full trapping series, 18 as partial trapping series, and 26 were classified as scientific estimate, with 4 series missing this information. When it comes to the series quality ID, 38 series had a quality ID of 1, indicating good quality, 40 had a quality ID of 0, indicating that it had been previously decided that the series should not be used in an analysis (usually because there were not enough years of data), and 21 series were missing a series quality ID. For the next WGEEL meeting, these series quality IDs should be reconsidered, given the large amount of series without a series quality ID, and the fact that some series with a quality ID of 0 now have at least 10 years of data. Almost all series had information on the potential impacts of restocking, with 21 series classified as being influenced by restocking and 35 as not being influenced by restocking.
The decision was made to perform the trend analysis with only those silver eel time series that had at least 10 years of data available. After examining the 57 available silver eel time-series, only 28 were kept for the trend analysis (Table @ref(tab:tablekept). From the 29 time-series that were excluded, 2 were showing inconsistencies in data and 27 were excluded because they did not have 10 consecutive years of effort data (Table @ref(tab:tabledropped).
The 28 silver eel time series which were used in the analysis represented six ICES ecoregions (Figure @ref(fig:mapsilverkept)). The Western Mediterranean Sea and Aegean-Levantine Sea only had one time series. The most represented areas were the Greater North Sea with 8 time-series and the Baltic Sea with 7 time-series. 11 ecoregions (Adriatic Sea, Arctic Ocean, Azores, Barents Sea, Black Sea, Faroes, Greenland Sea, Icelandic Waters, Ionian Sea and the Central Mediterranean Sea, Norwegian Sea, Oceanic Northeast Atlantic) did not have silver eel time series which were used in the trend analysis. All coastal time series used in the analysis are located in the Baltic Sea ecoregion. Freshwater series are located across 4 different ecoregions (Baltic Sea, Bay of Biscay and the Iberian Coast, Celtic Seas, Greater North Sea) and the transitional series are located in 2 ecoregions (Aegean-Levantine Sea, Western Mediterranean Sea).
Country | Series name | Years (n) | Series type | Divided by effort data | Comments |
|---|---|---|---|---|---|
BI1S | 16 | Index | No | ||
BI4S | 20 | Index | No | ||
NSIS | 22 | Index | No | ||
PanS | 16 | Index | No | ||
NO | ImsaS | 48 | Constant effort | No | |
SE | NkaS | 41 | Index | No | |
SE | SosS | 41 | Index | No | |
DE | WarS | 14 | Model estimate | No | |
DK | RibS | 22 | Model estimate | No | |
NL | HVWS | 10 | Index | No | |
NL | NiWS | 11 | Index | No | |
IE | BurS | 51 | Constant effort | No | |
IE | KilS | 23 | Effort-dependent | Yes | |
GB | BaBS | 17 | Constant effort | No | |
GB | FowS | 12 | Constant effort | No | |
GB | GiBS | 32 | Constant effort | No | |
GB | LevS | 21 | Constant effort | No | |
GB | ShiS | 20 | Constant effort | No | |
FR | BreS | 37 | Effort-dependent | Yes | |
FR | FreS | 27 | Constant effort | No | |
FR | LoiS | 34 | Index | No | |
FR | SeNS | 10 | Constant effort | No | |
FR | SouS | 10 | Model estimate | No | |
ES | AlCS | 68 | Effort-dependent | No | Commercial catches, but assumed that all eel are caught. |
ES | BidS | 13 | Constant effort | No | |
ES | NalS | 11 | Constant effort | No | |
ES | OriS | 16 | Index | No | |
GR | EamtS | 11 | Constant effort | No |
Country | Series name | Years (n) | Drop reason | Comments |
|---|---|---|---|---|
SE | KavlS | 4 | Number of years fewer than 10 | |
FI | KotkS | 6 | Number of years fewer than 10 | |
FI | VaakS | 9 | Number of years fewer than 10 | |
LV | DaugS | 4 | Number of years fewer than 10 | |
LV | LilS | 3 | Number of years fewer than 10 | |
LT | AlauS | 4 | Number of years fewer than 10 | Next year double check for available effort data on all similar Lithuanian series, and check if only silver eel are reported |
LT | CurlS | 5 | Number of years fewer than 10 | Next year double check for available effort data on all similar Lithuanian series, and check if only silver eel are reported |
LT | KertS | 4 | Number of years fewer than 10 | Next year double check for available effort data on all similar Lithuanian series, and check if only silver eel are reported |
LT | KreS | 1 | Number of years fewer than 10 | Next year double check for available effort data on all similar Lithuanian series, and check if only silver eel are reported |
LT | LakS | 2 | Number of years fewer than 10 | Next year double check for available effort data on all similar Lithuanian series, and check if only silver eel are reported |
LT | RieS | 1 | Number of years fewer than 10 | Next year double check for available effort data on all similar Lithuanian series, and check if only silver eel are reported |
LT | RubS | 2 | Number of years fewer than 10 | Next year double check for available effort data on all similar Lithuanian series, and check if only silver eel are reported |
LT | SiesS | 3 | Number of years fewer than 10 | Next year double check for available effort data on all similar Lithuanian series, and check if only silver eel are reported |
LT | ZeiS | 1 | Number of years fewer than 10 | Next year double check for available effort data on all similar Lithuanian series, and check if only silver eel are reported |
NL | BRWS | 8 | Number of years fewer than 10 | |
NL | DoijS | 8 | Number of years fewer than 10 | |
NL | IjsS | 8 | Number of years fewer than 10 | |
NL | NZKS | 7 | Number of years fewer than 10 | |
NL | ZMaS | 9 | Number of years fewer than 10 | |
GB | StrS | 6 | Number of years fewer than 10 | |
FR | VilS | 9 | Number of years fewer than 10 | |
PT | MinS | 5 | Number of years fewer than 10 | |
PT | MonS | 6 | Number of years fewer than 10 | |
IT | PobeS | 1 | Number of years fewer than 10 | |
IT | PogoS | 1 | Number of years fewer than 10 | |
IT | PolsS | 1 | Number of years fewer than 10 | |
IT | TibeS | 1 | Number of years fewer than 10 | |
GR | NorwS | 10 | Inconsistencies in data | Recent years reported as 0, but actually no information available |
GR | WepeS | 10 | Inconsistencies in data | Recent years reported as 0, but actually no information available |
Map of silver eel time-series used in the trend analysis, shown by ICES ecoregion and habitat.
Figure @ref(fig:figureseries) gives an overview of the reported CPUE data for each silver eel time series that was kept for the trend analysis. Among the kept series, the number of available CPUE data points was highest between 2010 and 2021, with the peak in 2013-2017 (Figure @ref(fig:figurenseries)). The majority of the kept time series did not have 2023 data ready at the time of writing this report.
CPUE data of those silver eel time series that were used in the trend analysis.
Number of available datapoints from silver eel CPUE time-series over time, shown only for those time-series that were used in the trend analysis.